1. Field of the Invention
This invention relates generally to implantable medical devices and, more particularly, to methods, apparatus, and systems for stimulating a cranial nerve of a patient to treat a medical condition, such as pulmonary disorders.
2. Description of the Related Art
The human nervous system (HNS) includes the brain and the spinal cord, collectively known as the central nervous system (CNS). The central nervous system comprises nerve fibers. The network of nerves in the remaining portions of the human body forms the peripheral nervous system (PNS). Some peripheral nerves, known as cranial nerves, connect directly to the brain to control various brain functions, such as vision, eye movement, hearing, facial movement, and feeling. Another system of peripheral nerves, known as the autonomic nervous system (ANS), controls blood vessel diameter, intestinal movements, and actions of many internal organs. Autonomic functions include blood pressure, body temperature, heartbeat and essentially all the unconscious activities that occur without voluntary control.
Like the rest of the human nervous system, nerve signals travel up and down the peripheral nerves, which link the brain to the rest of the human body. Nerve tracts or pathways, in the brain and the peripheral nerves are sheathed in a covering called myelin. The myelin sheath insulates electrical pulses traveling along the nerves. A nerve bundle may comprise up to 100,000 or more individual nerve fibers of different types, including larger diameter A and B fibers which comprise a myelin sheath and C fibers which have a much smaller diameter and are unmyelinated. Different types of nerve fibers, among other things, comprise different sizes, conduction velocities, stimulation thresholds, and myelination status (i.e., myelinated or unmyelinated).
Breathing functions are controlled by various cranial nerves that traverse portions of the human body. For example, the cranial nerve X (i.e., the vagus nerve) traverses down to the region of the lungs of the human body. The vagus nerve traverses down to the chest cavity forming the bronchial branches of the vagus nerve and traverses onto the pulmonary plexus. Breathing operation is controlled by the vagus nerve. The pulmonary plexus refers to the sites of convergence of autonomic fibers which supply the lung. Pulmonary plexus are located proximate the roots of the lungs.
There are various disorders relating to the operation of the lungs. For example, asthma is a chronic lung condition often characterized by difficulty in breathing. Generally, those with asthma tend to have extra-sensitive or hyper-responsive airways. These airways often react by narrowing or obstructing when they become irritated. This irritation causes air flow obstruction, such that movement of air may be restricted in the lungs. This may be exhibited by symptoms such as wheezing, coughing, shortness of breath, and/or chest tightness.
Bronchial constriction is a common result of asthma. Bronchial constriction refers to muscles that encircle the airways when they tighten or go into a spasm. State-of-the-art treatment for asthma generally includes various drugs, oxygen treatment, respiratory treatment, etc. Unfortunately, an asthma attack can occur at unexpected moments due to various reasons, such as allergies. Patients often carry various medication and inhalants to negate the effect of the hyper responsive reaction in the airways of the lungs.
Additionally, other breathing disorders, such as chronic obstructive pulmonary disease, also affect normal operation of the lungs. Chronic obstructive pulmonary disease (COPD) refers to a progressive disease of the airways. COPD may be characterized by a gradual attenuation of lung function. Various disorders that refer to COPD include chronic bronchitis, chronic obstructive bronchitis, emphysema, or a combination of any two or more of these conditions. COPD can be characterized by a substantially disabling shortness of breath. It is estimated that millions of patients suffer from such lung diseases. Lung disorders are often treated by various drugs. One problem associated with the state-of-the-art treatment includes a resistance that may build up to the drugs that are used to treat lung disorders. Additionally, some known drugs are not effective in certain patients. Besides drug regimens or invasive medical procedures, effective treatment for such diseases and disorders are fairly limited.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.